1. Field of Invention
The present disclosure relates to downhole pumping systems submersible in well bore fluids. More specifically, the present disclosure concerns a pumping system having a positive displacement pump where the pump reciprocatingly operates in response to expansion and contraction of an operating liquid.
2. Description of Prior Art
Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the well bore to the surface. These fluids are generally liquids and include produced liquid hydrocarbon as well as water. One type of system used in this application employs a electrical submersible pump (ESP). ESPs are typically disposed at the end of a length of production tubing and have an electrically powered motor. Often, electrical power may be supplied to the pump motor via wireline.
In many gas wells water (and possibly other liquids) is also produced with the gas. As the two-phase gas/liquid mixture enters the wellbore from the formation, the gas separates from the mixture and flows up the well through production tubing. Any liquid not trapped within the gas will flow down the wellbore and accumulate in the wellbore bottom. Accumulated liquid in the wellbore of a gas producing well can be a problem since it can reduce or prevent gas flow into the well. To overcome the liquid accumulation problem, dewatering techniques are often employed in water producing gas wells. Dewatering typically involves inserting a submersible pump in the wellbore to pump the liquid from the wellbore or producing a pressure differential between the wellbore and production tubing thereby forcing the liquid to the surface through the tubing.
One type of submersible pump for wellbore use comprises a centrifugal pump driven by a submersible electrical motor. The pump has a large number of stages, each stage comprising a diffuser and an impeller. Another type of pump, called progressive cavity pump, rotates a helical rotor within an elastomeric helical stator. In some installations, the motor for driving a progressive cavity pump is an electrical motor assembly attached to a lower end of the pump. Centrifugal pumps are normally used for pumping higher volumes of well fluid than progressive cavity pumps.